1. Field of the Invention
The present invention relates to a power converter such as an inverter using a semiconductor module.
2. Description of the Related Art
An occupied floor area can be downsized by arranging a semiconductor module on both surfaces of a cooler rather than a case in which the semiconductor module is arranged on only one surface thereof. However, when the semiconductor module is divided and arranged on both surfaces of the cooler, a connection between the semiconductor module and a control board is problematic. For example, in order to control the operation of a plurality of semiconductor modules synchronously, it is desirable to control the semiconductor module by one control board. In order to achieve this, as disclosed in JP-A-2005-73374, control terminals extend in parallel to surfaces of the cooler on which the semiconductor modules are mounted, and the control board is so arranged to face another surface of the cooler on which no semiconductor module is mounted. With this arrangement, the control terminals of all the semiconductor modules arranged on both surfaces of the cooler can be connected to one consolidated control board with the shortest length and with facility. Input and output wirings of the semiconductor modules, which are parts of a main circuit wiring, need to be arranged at an opposite side of the control terminals, that is, at an opposite side of a surface facing the control board of the cooler so as to concentrate the input wirings and the output wirings of the semiconductor module.
When the input wirings and the output wirings, which are parts of the main control wirings in which a large current flows, are concentrated and arranged, a space for arranging the output wirings in the vicinity of the input wirings, and a distance necessary for insulation between the respective wirings are required. Therefore, a smoothing capacitor connected to the input wirings cannot come close to the semiconductor modules. When the smoothing capacitor cannot come close to the semiconductor modules, a wiring inductance between the semiconductor element and the smoothing capacitor becomes larger. As a result, a switching surge voltage developed by a product of a current change rate caused by the switching operation of the semiconductor element and the wiring inductance becomes larger. When the switching surge voltage exceeds a withstand voltage of the semiconductor element such as the switching element or a reflux element mounted on the semiconductor module, the semiconductor element is broken down. Therefore, when the wiring inductance is large, there is a need to suppress the current change rate, that is, the switching speed and suppress the switching surge voltage. In this case, because the switching loss generated in the semiconductor element, that is, heating of the element becomes large, there arises such a problem that a large-sized cooler needs to be provided, or the power conversion efficiency is deteriorated. As another switching surge countermeasure, there is a method of adding a snubber circuit that suppresses the switching surge voltage. However, a space in which the snubber circuit is mounted is required, and it is difficult to downsize the power converter. As still another method, there is a method of limiting the input voltage of the power converter. However, this method suffers from such a problem that the performance of the power converter is sacrificed.
As compared with the structure of JP-A-2005-73374, in a structure of JP-A-2006-174572, although the semiconductor module is disposed on each surface of the cooler similarly, one control board is disposed to face each semiconductor module. Therefore, the semiconductor module in which the input wiring and the output wiring are disposed separately on two side surfaces is applied as disclosed in JP-A-2004-104860, the semiconductor module and the smoothing capacitor can be connected to each other with the shortest length, and the problem on the wiring inductance in JP-A-2005-73374 can be solved. However, in the structure of JP-A-2006-174572, because the control board can be divided into plural pieces, in order that the operation of the respective semiconductor modules is controlled synchronously, a control circuit and a power supply circuit are consolidated to the control board at one side, and the respective power conversion functions dispersed on both surfaces of the cooler are protected and get into synchronization, a unit for transmitting the signal between the control boards due to a harness connected through a connector mounted on the control board is required. In this case, the connector mounting space is required, and therefore a circuit scale that can be mounted on the control board decreases, the control board is upsized for mounting the required circuit scale, and a communication space of the harness is necessary. As a result, there arises such a problem that it is difficult to downsize the power converter. Also, the signal transmission distance between the control boards is long, and the influence of the noise is liable to occur. Therefore, even if the signal transmission speed between the control boards is sacrificed, that is, the performance of the power converter is sacrificed, measures that a filter is used for noise removal are required.
In configuring the power converter actually, there are required the semiconductor modules, the control boards that controls the semiconductor modules, and the cooler that cools the semiconductor module, as well as a smoothing capacitor that smoothes an input voltage of the semiconductor module, and the current detector for obtaining information used in the output control of the power converter, as exemplified by JP-A-2010-183749, JP-A-2006-81311, and JP-A-2005-12940. In the layout of those peripheral parts, various structures are proposed in JP-A-2010-183749, JP-A-2006-81311, and JP-A-2005-12940. For example, in the layout of the current detector, there is a need to connect an output control circuit that controls an output of the power converter by using current information detected by the current detector, and the current detector. However, the current information is very small as compared with the input and output voltage and current of the power converter, and it is desirable that attention is paid to adverse influence of noise, and the connection wiring is connected with the shortest length. Also, it is desirable to reduce the number of parts required for connection from the viewpoints of an improvement in the connection reliability and space saving.
In JP-A-2010-183749, a first control board having a driver circuit mounted thereon is disposed on the semiconductor module, a second control board having an output control circuit mounted thereon is disposed on the first control board, and the current detector is disposed at side surfaces of the semiconductor module and the first control board. The respective control boards and the second control board and the current detector are connected by the connector and the signal harness disposed at the current detector side of the second control board. However, because the connector and the signal harness are used, a space in which the connector is arranged, and a space for pulling the harness are required, resulting in such problems that it is difficult to downsize the power converter, and the assembling property is sacrificed by pulling the harness in a small space for downsizing.
Also, in a structure disclosed in JP-A-2006-81311, the semiconductor module and the current detector are aligned in the cooler, the control board having the output control circuit is so disposed as to cover the semiconductor module and the current detector, the current detector is connected directly to the control board by a lead pin disposed on the current detector. Thus, the structure is advantageous in downsizing because the connector and the signal harness are not provided. In order to reduce a stress generated in the terminal due to a temperature change or vibration in a limited height dimension between the control board and the cooler, the lead pin is curved in such a manner that after the lead pin extends in an opposite direction to the control board once, the lead pin is reversed and extends toward the control board. However, the complicated lead pin is guided, a fixed structure is required, and it is difficult to curve the lead pin when the device is further low in height, resulting in such a problem that it is difficult to make the height of the power converter lower.
In the layout of the smoothing capacitor, in order to obtain the power converter high in efficiency and small in size, it is necessary to reduce the wiring inductance as described above. JP-A-2006-81311 proposes a structure in which the semiconductor module is disposed on the cooler, the control board is disposed on the semiconductor module, the smoothing capacitor is disposed on the control board, and the smoothing capacitor and the semiconductor module are connected to each other on a side surface of the semiconductor module. However, the control board having a certain thickness including the parts height of the control circuit is interposed between the semiconductor module and the smoothing capacitor, and it is hard to say that the semiconductor module and the smoothing capacitor are connected to each other with the shortest length, and the wiring inductance is minimized. Also, when the semiconductor module is arranged also on a rear surface of the cooler for downsizing, not only the control board but also the cooler and the semiconductor module on the front surface side are also interposed between the semiconductor module on the rear surface side and the smoothing capacitor. As a result, the wiring inductance cannot be reduced, and a difference occurs in the wiring inductance between the semiconductor modules mounted on both surfaces of the cooler. The divided currents are not equal to each other when the semiconductor modules mounted on both surfaces of the cooler are driven in parallel, resulting in such a problem that heating of one semiconductor module becomes excessive.
Also, in JP-A-2005-12940, the semiconductor module and the smoothing capacitor are aligned in the cooler, and the semiconductor module and the smoothing capacitor can be connected to each other with the shortest length. However, when the semiconductor module are arranged on both surfaces of the cooler based on this structure, the smoothing capacitors also need to be disposed on both surfaces of the cooler. However, when a plurality of smoothing capacitors is disposed, the plurality of smoothing capacitors is connected in parallel. Resonance occurs due to an LC circuit consisting of a wiring inductance between the smoothing capacitors and capacitances of the respective smoothing capacitors, and an increase in a ripple current of the smoothing capacitor and an increase in size of the smoothing capacitor necessary for addressing this are problematic.
Also, the electrode surface of a small-diameter capacitor element is arranged orthogonal to the smoothing capacitor mounted surface of the cooler, and a plurality of capacitor elements is connected in parallel, and divided for each phase. With this structure, the height of the smoothing capacitor is lowered, and also the inductance is lowered. However, when the number of capacitor elements is large, the number of connections is larger, which makes it difficult to reduce the costs. If a plurality of parallel small-diameter elements for each phase is consolidated to one element for the purpose of reducing the number of connections for reduction of the costs, the element diameter becomes large, and the effect of the low height is lost. When the number of connections is reduced while the low height is kept, a plurality of slender elements with a small diameter is connected to each other. Therefore, the parallel structure for each phase unit becomes difficult, and the effect of the low inductance is lost. In addition, the small-diameter slender element is equivalent to an element having a small conductor sectional area (S) and a long path length (L), resulting in such a problem that the element heating (I^2R, R=ρ×L÷S) is large, and a permissible ripple current is small.